In the field of private mobile digital radio communication systems hereinafter called PMR system, there are a range of mobile terminals using a communication method so called PTT (for Push To Talk, or Press To Transmit). This communication method is made on a half-duplex link and based on pressing a button to switch or select the PMR terminal from a receiver report to a data transmitter report such as voice, especially, but more generally data of all kinds. Half-duplex link means a communication channel enhancing the data transport in both directions, but not simultaneously, in other words up-link (up-link in English) or in down-link (or down-link in English).
Push To Talk communication method is a voice over IP (for Internet Protocol) implemented in real-time Packet Data Networks. In other ways, a PTT terminal ensures a direct communication by pressing a button and establishes a link with a different terminal or multiple terminals.
The diagrams 1a-1c are the illustrations of a radio communication system 100 which are generally utilised for PTT terminals 110. In this radio communication system 100, a radio mobile PTT terminal 110 is typically interfaced to a network infrastructure 120 via multiple base stations 130 which are associated to site controller 135.
This network infrastructure 120 has one or more routing subsystems 140 which also known as regional networks. A routing subsystem 140 is considered to be the smallest subsystem that can provide PMR services 160 via an IP network 165. Each subsystem 140 has a switch which also called PTT server 150 has ability to manage the mobility of PTT terminals 110 on the network and to ensure the communication between PTT terminals 110 of that network. The PTT server 150 is also capable to be interfaced with one or more other PTT server 150, in order to ensure the multiple networking subsystems 140 between them and can cover a wide geographic area.
However, the current radio communication infrastructures in PTT technology are planned for terminals 110 which are operating on dial-up is known as narrowband (or Narrow Band in English). In other words, PMR services 160 may be accessible only for dial-up applications, or the modernisation of these PTT telecommunication infrastructures is necessary, in order to evolve broadband, is known as broadband (or Broad Band in English).
However, this modernization is long and complex to be implemented. In addition, there is also the interoperability problem between the two networks in order to communicate the dial-up terminals with high speed terminals and vice versa.